In Japan, point of view pornography is referred to as hamedori . Lying face down one may use the hands, one may straddle a pillow, the corner or edge of the bed, a partner leg or some scrunched-up clothing and hump the vulva and clitoris against it. Crush pornography features objects being crushed by an actress or actor, who generally plays an overtly dominant role. Female masturbation involves the stroking or rubbing of a woman vulva, especially her clitoris, with an index or middle fingers, or both. People may experience pleasure from anal sex by stimulation of the anal nerve endings, and orgasm may be achieved through anal penetration – by indirect stimulation of the prostate in men, indirect clitoral/G-spot stimulation in women, and associated porn milf sensory nerves . A 2009 study found that heterosexual male fat admirers preferred females that were clinically young gay porn overweight and rated both overweight and obese women more positively than slighter individuals. Ass to mouth is a slang term primarily used to describe the withdrawal of a penis from the receptive partner anus followed by the immediate insertion into the receptive partner mouth. Hentai narrow Japanese usage and broad international usage are often incompatible. These actors often play the top roles but this is not always the case, such as with Kristen Bjorn and some Bel Ami models. Sadomasochism refers to the aspects of BDSM surrounding the exchange of physical or emotional pain. A scene where many women have sex with one man is referred to as a reverse gang-bang. Particularly, some pornography in this genre features butch hentai videos women, who are almost never seen in mainstream pornography. See also Gay-for-pay. Diaper fetishism, nappy fetishism or diaperism, is a sexual fetish in which a person feels a desire to wear or use diapers. When early sexologists in the late 19th century began to categorize and describe homosexual behavior, hampered by a lack of knowledge about homosexuality or women sexuality, they distinguished lesbians as women who did not adhere to female gender roles and incorrectly designated them mentally ill—a designation which has been reversed in the global scientific community.